Product Code: 8520100 Research Personnel NAICS Code: 54171 Research and Development in the Physical, Engineering, and Life
Sciences

Persons:

Named Person: Seiler, Stephen

Geographic:

Geographic Scope: United States Geographic Code: 1USA United States

Accession Number:

297427065

Full Text:

We were somewhat surprised by the intensity of Frank Katch's
criticism of Stephen Seiler's History. Seiler defined the scope of
his presentation as the history of the current endurance performance
model: performance power = VO2max x (fractional utilization) x (work
efficiency) + (anaerobic capacity). Katch has done an admirable job of
complementing Seiler's history of this model with the earlier
history of endurance assessment. Seiler appears to have done justice to
the more recent history of assessment of oxygen uptake, although the
recent history of athletic performance testing in general still needs to
be written.

Katch also claims at the end of his critique that the proper
assessment of endurance performance "requires a new set of
parameters waiting to be discovered". Again, the theoretical basis
of the model and the practical application to athletes is also somewhat
outside the scope of Seiler's presentation. Indeed, Seiler made the
following comment to us during the review process: "I am trying to
publish something that has some utility as a teaching tool. In that
regard, I think it is great if it can be used as a starting point for
discussions of all these issues in the teaching setting." With that
comment in mind, we would like to support Katch's claim. There is a
sense in which the model described by Seiler has to be 100% formally
correct: for exercise at constant pace to exhaustion below VO2max
intensity, when multiplied together the three VO2 variables in the model
have to predict endurance power output exactly (without any anaerobic
term). In practice they don't, for two reasons. First, all three
variables require measurement of VO2, and VO2 has noise that is seldom
as low as 1-2% and often much worse. When you multiply all three
variables together, the noise compounds to around 3% or more, and when
you consider that the smallest important change in endurance power
output for a top athlete is ~0.3-1.0% (depending on the sport: Hopkins,
2004), it's clear the model isn't going to be particularly
useful. Noise in the variables and the fact that they all contribute to
endurance performance explains why individually they can have the low
correlations with performance that Katch referred to. The second reason
why the model doesn't work well is that fractional utilization is
seldom if ever measured directly as mean VO2 in the exercise divided by
VO2max: that measurement would require the athlete to breath into
respiratory apparatus throughout the exercise, and it's not
something athletes or researchers want to do. Instead, the surrogate
measures of lactate or ventilatory threshold are used. Although these
measures have the added bonus that they can be measured along with
economy and VO2max in a single incremental test, as surrogates they
introduce more error, not only because they aren't exactly the same
as fractional utilization, but also because they are probably more noisy
than fractional utilization.

So much for exercise below VO2max, but what about endurance above
VO2max? The current submaximal model can be applied to such exercise in
theory by setting the fractional utilization to 100%. You also have to
assume that economy remains the same as when measured submaximally,
because you can't measure it properly at or above VO2max. Anaerobic
capacity now enters the model, but the anaerobic capacity needs to be
divided by the duration of the exercise so that power outputs from
anaerobic and aerobic sources add up to the power demand of the
exercise. What we have now is the familiar critical-power model, which
is itself limited in its theoretical basis and practical application:
sweeping assumptions are required (summarized in Hinckson and Hopkins,
2005), and we know of no-one applying it in practice with athlete
assessment. Furthermore, the critical-power model does not make sense at
or below VO2max, even though misguided researchers have sometimes
applied it to such intensities.

So we agree with Katch that researchers need a new model,
especially one that works well for intensities around VO2max. The model
needs parameters that we can measure easily and accurately and that we
can train selectively. If, as seems likely, one or more of the
parameters is related to an intramuscular metabolite that builds up or
decays to some critical value (and is therefore responsible for
fatigue), use of the model with top athletes won't be practical
until a new technology allows the metabolite to be measured without
biopsies. Until then, empirical models of the way an endurance
athlete's performance changes with exercise intensity (e.g.,
Hinckson and Hopkins, 2005) are probably more useful than models that
depend on measurement of VO2.

References

Hinckson EA, Hopkins WG (2005). Reliability of time to exhaustion
analyzed with critical-power and log-log modeling. Medicine and Science
in Sports and Exercise 37, 696-701